For your first inquiry, the PPS is HIGH for every 1 second and stays for 1 microsecond. Also, the voltage is 2.85V.
Regarding your question about the optocoupler, our engineers stated that this may require optic coupler support because the 1PPS output is a very short pulse to be detected. However, using optic coupler does not ensure 1PPS detection.
Lastly, the maximum current of the PPS output is 2mA.